Such an ophthalmoscope is known from U.S. Pat. No. 4,765,730 and operates to scan the ocular fundus with high resolution. For this purpose, the light of a laser is deflected in two mutually perpendicular directions and is imaged on the eye of the patient. The light reflected at the ocular fundus transilluminates the same scanning unit in the opposite direction and is thereafter directed into a viewing beam path.
The scanning unit comprises two elements which scan the incident light beam in two mutually perpendicular directions. An imaging optic for compensating for astigmatism of the tilted concave mirror is provided between the two elements.
A telescope having a magnification different than 1x is provided between the concave mirror and the ocular fundus for changing the scanning region and thereby for changing the field of view. By exchanging the telescope lenses, it is then possible to switch the magnification over to the inverse value.
However, such a telescope, on the one hand, causes additional reflections at the telescope lenses which reduce the contrast of the viewed image. On the other hand, the additional components make the overall ophthalmoscope more expensive and the telescope furthermore increases that apparatus part of the ophthalmoscope which is to be aligned onto the eye of the patient.
U.S. Pat. No. 4,765,730 suggests an alternate possibility for changing the field of view. This possibility provides that the concave mirror is brought into a second position so that the scanning unit is imaged with another imaging scale on the eye of the patient. However, no information is provided as to what characteristics the switching positions should have or how the switchover between the switching positions should take place. In lieu thereof, it is stated that this alternative is difficult to realize.